The invention relates to the fabrication of semiconductor devices.
Semiconductor devices are typically fabricated on semiconductor wafers using silicon micromachining technology. Usually, each semiconductor wafer contains a large number of semiconductor devices, and each device may also be referred to as a “die.” In the context of semiconductor technology, a die is a small piece of semiconductor material, such as Electronic-grade silicon, on which the device, such as an integrated circuit, is fabricated. During a typical fabrication process, a large batch of the devices is fabricated on a single wafer. The resulting wafer is cut into many small pieces, and each piece, called a “die,” contains a copy of the device.
Often, each individual die contains moving mechanical parts that are required to be free to be operational. These moving mechanical parts are fabricated using the same semiconductor wafer and are attached to the die at one or more ends. The dies are in turned attached to a frame on the wafer by means of holding tabs to form a wafer assembly. The frame and the holding tabs are part of the micro-fabrication process and are fabricated simultaneously with the devices.
FIG. 1A illustrates a method of holding multiple semiconductor devices in a wafer assembly. FIG. 1B illustrates a backview of a magnified portion of the wafer assembly illustrated in FIG. 1A. Referring to FIGS. 1A and 1B, the wafer 100 contains multiple semiconductor devices 110 neatly lined up. Each device 110 is connected to one or more frames 120 by means of one or more holding tabs 130. That is, each device 110 is connected to one or more holding tabs 130, which in turn are connected to one or more frames 120. Gaps 140 exist between the devices 110 and the frames 120. The individual devices 110 are removed from and break free of the frames 120 by breaking the holding tabs 130. To do so, one may insert a pair of tweezers inside a gap 140, grab hold of a device 110, and firmly pick it out by applying a torsional force, breaking the holding tabs 130 in the process. Alternatively, one may press the device 110 downward until the holding tabs 130 break and then grab the device 110 with a pair of tweezers to lift it out of the frames 120.
In order to maximize the number of devices 110 per wafer 100 to reduce the cost of fabrication per die, the gaps 140 between the devices 110 and the frames 120 must be kept as small as possible. This necessitates the use of a pair of tweezers with extremely fine ends for the singulation process (breaking the devices 110 free of the frames 120). The edges of the devices 110 are normally very sharp due to etching and sharpening processes, and these sharp edges break easily while grabbing the devices 110 with the pair of tweezers. This results in a large number of fine silicon splinters, which are very fine particles, coming out of the devices' edges. The splinters may directly damage the devices 110 or electrostatically stick to the devices 110 to make them inoperational.
FIG. 2A illustrates another method of holding multiple semiconductor devices in a wafer assembly. FIG. 2B illustrates a back view of a magnified portion of the wafer assembly illustrated in FIG. 2A. Referring to FIGS. 2A and 2B, the wafer 200 contains multiple semiconductor devices 210 neatly lined up. Each device 210 is connected to one or more frames 220 via a single tab 230 terminated with a V-groove. The V-groove is formed while etching the wafer from the backside in a wet chemical anisotropic etching solution. The thickness of the semiconductor material, such as silicon, left after the V-grove termination is critical. To separate a device 210 from the frame 220 it connects to, pressure is applied at the point where the V-grooves meet. However, since the pressure is applied only at one side of the device 210, the device 210 has a tendency to flip over and may damage the delicate device 210. The gap and sharp tweezer argument is also valid for this arrangement.
Accordingly, what is needed is a system and a method to address the above-identified problems. The present invention addresses such a need.